US Patent 10882135 Apparatus for additively manufacturing of three-dimensional objects

An apparatus for additively manufacturing three-dimensional objects includes a scanning unit configured to scan an energy beam over a build plane, and a focusing unit that includes an optical lens or lens system. The focusing unit may be configured to control a focal position of the energy beam based on calibration information. The focal position may be controlled by moving the focusing unit in the z-direction relative to the build plane without changing the focal length of the energy beam. Methods of calibrating such an apparatus may include moving a focusing unit in the z-direction relative to a build plane based on calibration information and scanning an energy beam over at least a portion of the build plane using a scanning unit, with the focusing unit being configured to control a focal position of the energy beam without changing the focal length of the energy beam.